arrays - Looking to parse EMV data into TLV

Question

Okay - I have this hex data and I have a list of tags:

the raw data may look like this:

5F201A54444320424C41434B20554E4C494D49544544205649534120204F07A00000000310105F24

Because I have a list of tags I can see there are multiple values here Tags [5f20, 4f, 5f24]

Ex: 5F201A54444320424C41434B20554E4C494D49544544205649534120204F07A00000000310105F24…ETC

So - I know that I have this tag [5f20] and its value is all the other stuff in between [5f20] and [4f]. —

I can take this other stuff:

1A54444320424C41434B20554E4C494D4954454420564953412020 and create a string from it which becomes: ("TDC BLACK UNLIMITED VISA“)

I can parse through a small section of it like using:

    let string2 = 
    "5F201A54444320424C41434B20554E4C494D49544544205649534120204F"
    var string3: String = ""
    if let startRange2 = string2.range(of: "5F20"),
    let endRange2 = string2.range(of: "4F")
    {
    let contents2 = String(string2[startRange2.upperBound..
    <endRange2.lowerBound])
    print(string3)
    string3 = contents2
    }

What Im not sure about is: How do I scale this up to work with data where I wont know what tag will be first or second or how many there are? Im seriously stumped and I don't know where to go from here.

Overall my goal is to get create readable data like this: Clean formatted Tags and value

look something like this:

5F201A54444320424C41434B20554E4C494D49544544205649534120204F07A00000000310105F24032307319F160F4243544553542031323334353637389F21031826509A031406179F02060000000000019F03060000000000009F34030203009F120C56495341204352454449544F9F0607A00000000310105F300202019F4E0F616263640000000000000000000000C408491573FFFFFF1097C00A09117101800165E0000AC2820168D9DE289AAD770BE408F6B1D4E0A2576CEA7F03CD479CE3A1827375D6C4D4959ACDB5D3B6F84CD83430F4346C35E48A77A0D5F36FBEA444C2D8701C07FFC7AF06C0485D68F7A83FC30840D3C0766EC4EE669BE5A42BAD4C7459680FAAAE9C4EFEFFEB5A590E53B3E91B3CD28A415C2C9484E26DA5A15592BBCD1F45CF49D27A9D480B031957DF8C790C55FF60DB192CCD070FA4F7BCDC99E7F7567C2F991B5536F9336BA66D68115D54BC3642A9CA47FDD162FCDC33E455AAC283975DACC98CBE9A6611E996F0740072CF8E32D3D9F39F4BB25568F5CC3E7F5DE158E4D62BF4E7185CF13BD068C4F062C26A3BBF88E056F249130E89AA29E52A1EBB6BAD98296822F10949F0C825D1449DA7EF4431AB846D0DDB916F2901359DD9A3B3395BAC9F9BE4D24657F65B030DDADA53577A14D9F5F776B6FF7EAB99D8C4BB08BEF2016C72D94B1DB91BCF0238405B7857646DCE5F79871D96B6A6652090FD8CFCC59973433919A6D0533DFE

Answer 1

所以你可以有三个数组。一个数组包含所有短标签，一个数组包含所有长标签，一个数组包含所有专有标签。

您可以使用您创建的三个标签数组遍历您的长字符串。

首先用你的短标签数组检查长字符串，这是前2个字符，如果它们不在你的短标签列表中，然后取前4个字符检查它是否是长标签，如果它不在长标签中标签列表要么是专有标签。

例如你的字符串，

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

你将取前两个字符 5F，用它来循环你的短标签数组，看看是否有匹配，没有匹配。

既然没有匹配，你就重新开始检查它是​​否是一个长标签，所以长标签总是4个字符，所以你取前四个字符是5F20。

循环遍历您的长标签以查看是否有 5F20。是的，所以 5F20 之后的两个字符就是你的长度。所以1A是你的长度。我知道 1A 更长，因为标准格式总是

标签 | 长度 | 价值

现在您知道您的长度是多少，使用该长度来确定您的值中有多少个字符。1A 转换为 int 是 26，你总是将长度乘以 2。所以你的值将包含 26 x 2 = 52 个字符，从 1A 之后的字符开始。

所以这将是你的价值 54444320424C41434B20554E4C494D4954454420564953412020

将该十六进制转换为您得到的字符串：TDC BLACK UNLIMITED VISA

遵循该结构将获得您的所有标签、长度和值。

Answer 2

任何 EMV 标签都遵循以下标签长度及其值的标准。它取自 EMV Book 3。从 EMVCo 网站的规格部分下载。